A comparison of Direct Gasoline Injection (DGI) and Port Fuel Injection (PFI) shows that both concepts offer advantages for certain operating conditions.
PFI provides a homogeneous mixture due to the longer time which is available for mixture preparation. This ensures a good and stable combustion. As already mentioned DGI is advantageous in terms of driveability and transient engine behaviour, leads to an increased volumetric efficiency, ensures lower emissions and a higher compression ratio can be realised which leads to a higher performance.
So it is logically to make use of the advantages of both concepts by a combination of DGI and PFI. In picture 'Optimal ration between DGI and PFI for maximum performance' the optimal ratio between DGI and PFI for maximum engine performance and the possible performance increase for one operating point by DGI - PFI compared to DGI only or PFI only is shown. This ratio is different for each operating point. The possible performance increase over engine speed by DGI - PFI is described in picture 'Performance increase by DGI - PFI'.
Picture 'DGI - PFI engine concept' shows a V2 engine concept with one top feed injector and one direct injector per cylinder. The direct injector is placed under the intake port between the intake valves.
Using two injectors is also advantageous to cover the required dynamic range from idle operation to wide open throttle at rated speed.
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